The main issue to be aware of when bonding 7740 to oxidised silicon is the
large difference in electrical resistivity between 7740 and SiO2. This
results in a large proportion of the applied voltage being dropped across
the oxide rather than the glass, and can lead to electrical breakdown of the
oxide layer. However during the anodic bonding process a depletion layer is
generated in the glass, at the oxide interface, and this layer becomes more
and more resistive as the process continues. Thus the proportion of the
applied voltage that is dropped across the oxide reduces with process time
hence enabling higher voltages to be applied. By operating in a current
limited bonding mode it is possible to bond to oxidised silicon without risk
of electrical breakdown in the SiO2. In the standard AML current limited
bonding process the voltage increases gradually and only reaches set point,
typically 1200V for a 410C process temperature, once the glass depletion
layer is sufficiently formed. Using this technique we have successfully
anodically bonded to silicon wafers with oxide layers greater than a micron.

Regards

Tony Rogers

-----Original Message-----
From: Charles
Subject: [mems-talk] Anodic bonding oxidized Silicon wafers to Glass

We have sucessfully bonded pyrex 7740 and borofloat glasses to bare
silicon wafer many times (so we have the equipment and some
understanding). We are now developing a process which requires attaching
pyrex 7740 glass to an oxidized silicon wafer.  The oxide will be 200nm
or so thick.  Does anyone have experience with this type of anodic
bonding? Is it possible? Any suggestions?